I installed the demo of the OFX version to compare it to my purchased NV4. The NV5 demo and purchased NV4 are available in Fusion Studio 9.0.2, but is not there in Davinci Resolve Studio 15.3. I only see the NV4 version in Resolve, not both NV4 and NV5.

Please check the upgrade options in your account. You will find that the bundle upgrade is not that much more expensive that the OFX upgrade (and certainly less expensive than OFX upgrade plus Resolve upgrade added up). In the older versions, there were no those individual options.